Process for producing photographs in natural colors



April 23,1929. w. LANGGUTH ET AL PROCESS FOR PRODUCING PHOTOGRAPHS IN NATURAL COLORS Filed Aug. 29, 1927 I155 dttozmago.

Paste-.1 Apr. 23, 1929.

. UNITED STATES 1,710,455 PATENT" OFFICE.

WERNER LANGGUTH, OF THUR, AND CHARLES HUMMEL, OF lIIEDER-UZWIL,

SWITZERLAND.

PROCESS FOR PRODUCING PHOTOGRAPHS IN NATURAL COLORS.

Application filed August 29, 1927 Serial No. 216,334, and in Germany July 9, 1926.

light filters to the object to be photographed.

A suitable support, for instance a sheet of pure unsized and chromated paper, is saturated with suitable azo-dyestutf components and is exposed in still moistcondition under the negative which was taken behind the red light filter. Since this exposure, which is preferably in direct sunlight, raises the temperature of the-sensitive paper, which rise oftemperature is disadvantageous to the development of the color, the paper is best exposed in a printing frame 'Which is'cooled by water. This water-cooling can also be connected with the light filter, to be mengioned later, by forming the latter as a liquid lter.

By the action of the light, which action should be controlled by a suitable light filter, there is produced on the paper a blue-green picture. This is then washed in water, in

' which the unexposed azo-dyestuff components are dissolved, so that the picture is permanent. The paper is then saturated with other azo-dyestulf components and exposed again under the negative corresponding with .the violet light filter, care being taken to 40 ensure careful'registration of the first picture with the second. In this manner there is produced upon the blue-green picture a yellow picture. In similar manner the third, purple, component picture is produced.

In the accompanying drawing Fig. 1 shows, 0. g, a green-blue picture corresponding to the negative which wastaken -behind the red light filter. Fig. 2 represents'the state of the copy after the yellow picture (which corresponds to the negative taken behind the violet light filter) has been copied onto the green-blue picture, and Fig. 3 is the combined color picture consisting of the picture as representedin Fig. 2 and of the purple plcture.

For the purpose of protecting the negafinished picture with a solution of a trans-" parent colorless solid body, for instance a cold solution of a fatty oil or of a resin or a of a balsam or of collodion, or a hot solution of agar-agar or gelatine; when such a solution dries the paper fibre and the dyestuff are united to a homogeneous whole. Owing to this aftertreatment the light falling'upon the picture can penetrate further into the paper surface and is therefore reflected in stronger color; at the same time the picture becomes more fast to light.

By right choice of 'azo-dyestu'if components (direct-dyeing dyestuffs, substantive azo-dyestufis) dyes are obtained which dye uniformly the paper fibre of the support. The dyes penetrate each separate fibre and by this direct mixing of'the fundamental colors, mixed colors are produced which couldnot be obtained so completely merely by the superposition of differently colored layers.

The control of the covering power of thedifl'crent color pictures is very simple, since the pictures are produced on the same support and may printing frame.

The order of succession in which the scparate pictures are printed, namely first the green-blue, then the green-yellow and then the purple, is to be followed exactly since he observed directly in the otherwise filtrating of the light by the first printed colors may occur which will affect the conditions of the azo-dyestuffs and the brightness and naturalness of the mixed colors.

The light filters used in the exposure are advantageously of color complementary to that of the component picture to be ob tained. As az o-dyestufi' components which afford three substantive. azo-dyestufis the following have been found especially suitable-For the reen blue picture: salts of dianisoltetrazodisulphonic I acid and 1.8-

a support, saturated with azo-dyestu aminonaphthol-2.4-disulphonic acid; for the green-yellow picture: salts of methylbenzidinetetrazodisulphonic acid and acetoacetic acid CILCOCH COOH, or an ester or anilide derived therefrom; for the 'purple picture: salts of anisidinediazosulphonic acid and oxynaphthoic acid or derivatives thereof, such as esters.

\Vhat we claim is:

1. In a process for producing photographs in natural colors of the kind in which three component pictures in the fundamental colors are successively printed on the same support, azo-dyestuif components being used as substances sensitive to light, the improvement which consists in ex osing components, while still moist under the negatives in a printing frame having a cooling device, the printing of the composite picture being in the order of succession: first the green-blue, then the green-yellow and finally the purple picture, the exposure of the several composite pictures being under a light filter of color complementary to that of the component picture to be printed, that is to say the green-blue component under a yellow light filter, the green-yellow under a violet and the purple under a blue.

2. In the process referred to in claim 1 the employment onlyof substantive colors.

3. In the process referred to in claim 1 the. employment of the following components: for the blue picture salts of dianisoltetrazodisulphonic acid and 1.8amino I12l])llt-ll0l-2.4-(llSllll)l10Hl0 acidfor the yellow picture salts of methylbenzidinetetrazodisulphonic acid and aceto-acetic acidt'or the red picture salts of anisidinediazosulphonic acid and oxyna )hthoic acid.

4. In the process re erred to in claim 1 the employment of the following components: for the blue picture salts of dianisoltetrazodisulphonic acid and 1.8- alninonaphthol-ZA-disulphonic acidfor the yellow picture salts of the derivatives of Inethylbenzidinetetrazodisulphonic acid and derivatives of the aceto-acetic acidt'or the WERNER LANGGUTH. CHARLES HUMMEL. 

